RE: Sundowner questions
just to clarify, your prop selection with the OS46 is important too. You have to balance the needs of the engine and airframe.
When you add performance using a tuned exhaust or tuned pipe, you have to select a prop that balances the engine/airframe/exhaust system.
So yes, the prop selection is critical for the tuned exhaust. The muffler has an RPM range where the tuned effect boosts power. In this case, You want to prop the OS46AX engine to run between 14,500 and 16,000 peak ground rpm to obtain best performance.
The 4c engine is RPM limited. So its the same deal with prop selection. You have a max target rpm (10,000 ?). You have to prop to the performance target, while also finding the best aircraft performance.